Theorem chjvali

Description: Value of join in CH . (Contributed by NM, 9-Aug-2000) (New usage is discouraged.)

	Ref	Expression
Hypotheses	chjval.1	$$⊢A\in {\mathbf{C}}_{\mathscr{H}}$$
	chjval.2	$$⊢B\in {\mathbf{C}}_{\mathscr{H}}$$
Assertion	chjvali	$$⊢A{\vee }_{\mathscr{H}}B=\perp \left(\perp \left(A\cup B\right)\right)$$

Proof

Step	Hyp	Ref	Expression
1		chjval.1	$$⊢A\in {\mathbf{C}}_{\mathscr{H}}$$
2		chjval.2	$$⊢B\in {\mathbf{C}}_{\mathscr{H}}$$
3		chjval	$$⊢\left(A\in {\mathbf{C}}_{\mathscr{H}}\wedge B\in {\mathbf{C}}_{\mathscr{H}}\right)\to A{\vee }_{\mathscr{H}}B=\perp \left(\perp \left(A\cup B\right)\right)$$
4	1 2 3	mp2an	$$⊢A{\vee }_{\mathscr{H}}B=\perp \left(\perp \left(A\cup B\right)\right)$$